With developments of technologies, smart phones are used more and more widely and have more and more functions, and hence have become necessary electronic devices in people's daily lives. At present, a large display area of a mobile phone can better meet users' requirements of browsing webpages, reading, watching films, playing games and so on. Accordingly, the current smart phone has a larger screen, and a full-screen phone comes into being. The full-screen phone employs a flexible screen, and a cover plate joined to the flexible screen will pull the flexible screen when the phone falls down, thus causing the flexible screen to be delaminated and cracked easily.